The large-scale study, published in Nature, could help to target new ways of preventing and treating these diseases. It concluded that a substantial proportion (at least one-sixth) of the variation in birth weight is down to genetic differences between babies. This is seven to eight times more variation than can be explained by environmental factors already known to influence birth weight, such as the mother smoking during pregnancy or her body mass index (a measure of obesity) before pregnancy starts.

It has been known for some time that babies whose birth weight is well below, or well above, average have a markedly increased risk of diabetes many decades later. Until now, many researchers have assumed that this link reflects the long-term impact of the nutritional environment in which the foetus develops: in other words, that events in early life can “set up” an individual’s body in ways that make them more prone to disease in later life.

In this new study, the researchers uncovered a substantial overlap in the genetic regions linked to differences in birth weight and those that are connected to a higher risk of developing diabetes or heart disease. Most of this overlap involves the baby’s genetic profile, but the team found that the mother’s genes also played an important role in influencing her baby’s birth weight, most likely through the ways in which they alter the baby’s environment during pregnancy.

Professor Mark McCarthy at the University of Oxford, and co-lead author, said: “These findings provide vital clues to the some of the processes that act over decades of life to influence an individual’s chances of developing diabetes and heart disease. These should highlight new approaches to treatment and prevention. Understanding the contributions of all of these processes will also tell us how much we should expect the many, wonderful improvements in antenatal care to reduce the burden of future diabetes and heart disease”.

Dr Nicholas Timpson at the University of Bristol, and co-lead author, said: “The work does not necessarily show that birth weight itself is a direct target for potential therapeutic intervention, rather that there are likely to be shared mechanisms between the complex set of biological events contributing to birth weight and those to later life health. It was great that the Avon Longitudinal Study of Parents and Children was able to contribute to this work in such a substantial manner.”

The researchers analysed genetic differences throughout the genomes of nearly 154,000 people from across the world. Around half of these came from the UK Biobank cohort. By matching the genetic profiles of these people to information on birth weight, the researchers could identify 60 regions of the genome that were clearly driving differences in birth weight. They then analysed data from previous studies on conditions including diabetes and heart disease, and found that many of the same genomic regions were implicated.

Further information

Based at the University of Bristol, Children of the 90s, also known as the Avon Longitudinal Study of Parents and Children (ALSPAC), is a long-term health-research project that enrolled more than 14,000 pregnant women in 1991 and 1992. It has been following the health and development of the parents and their children in detail ever since and is currently recruiting the children and the siblings of the original children into the study. It receives core funding from the Medical Research Council, the Wellcome Trust and the University of Bristol. Find out more at www.childrenofthe90s.ac.uk